The excavating machines of the prior art generally include digging wheels having a series of circumferentially spaced buckets which usually have a transverse dimension appreciably greater than the dimension of the tile to be laid. The resulting extra ditch width is often necessary for machine clearance purposes but the extra power and time required in digging and filling the extra width ditch materially increases operational costs. Such type machines are generally disclosed in U.S. Pat. Nos. 1,064,733; 1,113,952; 1,199,366; 1,215,791; 2,730,821; 2,914,866 and 3,077,042. These machines generally operate with difficulty in hard or frozen ground due to the tendency of the buckets to ride on, rather than to penetrate into, the surface being worked on. This riding tendency results in appreciable bouncing of the machine and instability in its operation. Additionally, only a portion of the effective peripheral surface of the digging wheel is utilized for conveying spoil to the surface whereby the linear advance of the machine in a digging operation takes place at a relatively slow rate of speed.
The digging machine of U.S. Pat. No. 3,412,490 is constructed for the high speed digging of a narrow ditch for the laying of cables and the like of small diameter with the disposition of the spoil being to each side of the ditch. However, the volume capacity of the machine for handling spoil is necessarily limited by the open spiral arrangement of the digging teeth about the peripheral surface of the digging wheel. The trenching machine of Radahl Industries of Rakkestad, Norway, as disclosed in literature therein, has a digging wheel with a single circular channel way open to one side of the wheel with the outer peripheral side wall of the channel being comprised of a plurality of circumferentially arranged curved segments, the adjacent ends of which are spaced apart radially of the wheel to form spoil receiving inlets. This machine performs well in both hard and soft terrain and is capable of digging a narrow trench. However, since spoil is carried only on one side of the wheel, the rate of travel of the digging operation and the depth of the ditch being dug are limited.
U.S. Pat. No. 3,680,919 discloses a digging wheel adapted for digging in both hard and soft terrain by the provision of a relatively large number of buckets and the use of detachably mounted weight members for selectively controlling the inertia of the digging wheel.